Udakūpama Sutta

There are seven kinds of people in the
world who are like objects that fall into wells: Some having sunk into the water
remain there; others continue sinking and rising; some having risen once will
not sink again; others having risen will look round, etc. Similarly, some having
fallen into sin never escape there from, others are prone to weakness but often
check themselves, etc. A.iv.11-13.